Sandwich stent

ABSTRACT

A stent is made generally tubular and is initially formed in a collapsed configuration. A fabric cover is provided for the inner stent and is attached outside the stent at one or more desired locations. The fabric cover is much larger in diameter than the diameter of the collapsed stent, however, when the stent is expanded through activation of the balloon catheter therewithin, the stent expands to closely conform to the interior walls of the fabric cover. The attachment of the fabric cover and the stent may be accomplished in several ways. In one embodiment, the fabric cover may be attached outside the inner stent at one linear location parallel to the axis of elongation of the stent. In an alternative embodiment, the fabric cover may be attached concentrically about the inner stent and secured in that configuration by a series of sutures. In a further modification, the fabric cover may be attached around the inner stent non-concentrically through the use of suitable sutures. In a first alternative, one or more expandable clips are collapsed about the fabric cover to secure it about the inner stent. When the entire stent sandwich is expanded, these clips expand as well and comprise stents themselves. In a second alternative, securement of the fabric cover or intermediate stent layer about the inner stent is accomplished through the use of a wire spiraling externally about the outer surface of the fabric cover to secure the fabric cover or intermediate stent layer about the inner stent. When the stent sandwich is expanded, the configuration of this spiraling wire permits it to expand as well and lie against the inner walls of the blood vessel at the desired location. The stent has spaced ends, each of which may be coated or otherwise provided with a radio-opaque material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stent. More particularly, it relatesa sandwich stent which provides a mechanical barrier for prohibiting thegrowth of tissue through an artery implanted stent.

2. Description of the Prior art

In the prior art, stents are well known for use in minimally invasivesurgery or interventional procedures for attaching to the inner walls ofa blood vessel where a procedure such as a balloon angioplasty has beenperformed. Such prior art stents are essentially metallic scaffolds thatare left in the arteries to prevent the arteries from collapsing back totheir original form due to a phenomenon called elastic recoil. Suchrecoil can be common after the dilatation of a balloon.

Although the subject prior art stents have been generally successful inpreventing elastic recoil, they have not been successful in theprevention of instent restenosis. Such phenomenon occurs when tissuegrows into and through the struts of the stent due to openings in thestent struts. The tissue is then permitted to grow into the lumen andreocclude the artery, whereby a balloon angioplasty procedure most berepeated.

In an effort to prohibit instent restenosis, stents were provided withcovering material. Such can be seen in U.S. Pat. No. 5,562,728 toLazarus et al. wherein a helical wrap of ribbon is attached to acovering material; the attachment being only at the ends. U.S. Pat. No.5,578,071 to Parodi et al. show a vascular graft that has two stentsattached at the ends of the tubular conduit, where at one wire isprovided and woven into a distal end, or lower end, of the graft, thewire permitting the distal end of the graft to conform to and sealinglyengage within the artery of the patient.

When conveying a stent to its point of use, it is imperative that anycovering material be secured about the stent in a secure and tightfashion to preclude the stent from being "hung up" in some area of thevascular system of the patient while it is being conveyed to the pointof use. The prior art stents do not adequately secure the cover to thestent to prohibit such hang up. Further, the prior art devices have avery large profile that require being cut down by a surgeon and insertedinto the body through a very large opening. Accordingly, minimallyinvasive surgery, in its strictest meaning, is not provided. Because ofthe large profile, the prior art devices are not useable in every areaof the body, but only in larger arteries.

A stent is needed that overcomes the problems in the prior art. Such astent needs to be low in profile yet provide the necessary mechanicalbarrier to prevent instent restenosis. An improved means of securementis needed to prevent the covering material hang up. Further, providingsuch an improved stent with a low profile can be used in widespreadapplications and not be limited to large artery procedures.

SUMMARY OF THE INVENTION

The present invention relates to embodiments of a sandwich stent. Thepresent invention includes the following interrelated objects, aspectsand features:

(1) In a first aspect, an inner stent in accordance with the teachingsof the present invention is made generally tubular and is initiallyformed in a collapsed configuration. A balloon catheter may be containedwithin the collapsed stent and inflation of the balloon catheter at thesite of installation causes the stent to expand to its expandedconfiguration lying closely against the inner walls of the desired bloodvessel.

(2) A cover is provided for the inner stent and is attached outside thestent at one or more desired locations. An internal diameter of thecover is equivalent to the size of the artery in which it is beingintroduced. Since the cover is attached to the inner stent, when thestent is expanded by the balloon catheter, the stent expands to theinternal diameter of the cover which happens to be the diameter of theartery. Hence, the covered stent conforms to the interior wall of theartery positioning therewithin.

(3) The attachment of the cover to the inner stent may be accomplishedin several ways. In one embodiment, the cover may be attached outsidethe inner stent at one linear location parallel to the axis ofelongation of the stent. In an alternative embodiment, the cover may beattached concentrically about the inner stent and secured in thatconfiguration by a series of sutures. In a further modification, thefabric cover may be attached around the inner stent non-concentricallythrough the use of suitable sutures.

(4) The cover, also comprising an intermediate stent layer, is suitablycollapsed and pleated so that it closely surrounds the inner stent. Thepresent invention contemplates two exemplary embodiments of securementmeans for securing the cover or intermediate stent layer about the innerstent. In a first alternative, one or more expansible clips arecollapsed about the cover to secure it about the inner stent. When theentire stent sandwich is expanded, these clips expand as well andcomprise stents themselves. The slow expansion of the clips facilitatesthe unpleating or unraveling of the cover. Without such clips, the covercould have several folds and crimps upon expansion, hence, a potentialfor hang up. The clips facilitate uniform expansion and also assist inmaintaining cover integrity. In a second alternative, securement of thefabric cover or intermediate stent layer about the inner stent isaccomplished through the use of a wire spiraling externally about theouter surface of the cover to secure the cover or intermediate stentlayer about the inner stent. When the stent sandwich is expanded, theconfiguration of this spiraling wire permits it to expand as well andlie against the inner walls of the blood vessel at the desired location.

(5) The stent has spaced ends, each of which may be coated or otherwiseprovided with a radio-opaque material. A cardiologist or surgeon mayinsert the stent and view its progress through the vascular system ofthe patient with equipment such as, for example, an X-ray device toensure that the stent is properly traveling toward the location ofinstallation and is precisely located at its final destination.

Accordingly, it is a first object of the present invention to provide asandwich stent.

It is a further object of the present invention to provide such a stentincluding an inner stent, an intermediate stent comprising a cover andan outer stent comprising securement means for securing the cover aboutthe inner stent.

It is a still further object of the present invention to provide such astent wherein the cover is secured about the inner stent from within thecover in any one of several ways.

It is a still further object of the present invention to provide such asandwich stent wherein the cover is secured about the inner stent fromthe outside therefrom in one of a plurality of possible ways.

These and other objects, aspects and features of the present inventionwill be better understood from the following detailed description of thepreferred embodiment when read in conjunction with the appended drawingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side perspective view of one embodiment of the inventivestent.

FIG. 2 shows a cross-sectional view along the line 2--2 of FIG. 1.

FIG. 3 shows a cross-sectional view along the line 3--3 of FIG. 2.

FIG. 4 shows a view similar to that of FIG. 2 but with the fabric stentcover folded and collapsed about the stent body.

FIG. 5 shows the inner stent of FIGS. 1-4 with a delivery device such asa balloon catheter inserted therein.

FIG. 6 shows the stent and delivery device of FIG. 5 with the cover orintermediate stent layer placed thereover.

FIG. 7 shows the stent sandwich of FIG. 6 with the outer layerconsisting of a plurality of narrow stent bands secured about the coveror intermediate stent layer as the entire stent assembly travels througha blood vessel.

FIG. 8 shows the stent assembly expanded at a desired location within ablood vessel with the delivery device being removed.

FIG. 9 shows a view similar to that of FIG. 2 but with an alternativemeans of securement of the cover about the inner stent.

FIG. 10 shows a further modification as compared to the views of FIGS. 2and 9.

FIG. 11 shows a view similar to that of FIG. 7 but depicting analternative outer securement means overlying the cover or intermediatestent layer.

FIG. 12 shows a view similar to that of FIG. 8 but depicting the stentassembly of FIG. 1 as expanded within a blood vessel and with thedelivery device being removed therefrom.

SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference, first, to FIG. 1, a stent is generally designated by thereference numeral 10 and is seen to include an inner stent 11 and acover or intermediate stent layer 13. The inner stent 11 is seen to betubular in configuration and is shown in FIG. 1 in its collapsedconfiguration. In the preferred embodiment, the cover 13 is a wovenfabric. But, other materials can be used. Further other forms ofmanufacturing can be used such as knitting, extruding, coextruding,braiding, interweaving, or interlocking. Cover 13 may also carry abioactive or bioinactive substance.

As seen in FIG. 2, the cover 13 is attached to the inner stent 11 at onelinear location 15 on the inner stent. The reference numeral 15 is usedin several locations in FIG. 1 to show the linear nature of theattachment location of the cover 13 on the inner stent 11. Attachmentmay be accomplished through any suitable means such as, for example,surgical staples, sutures, adhesion, imbedding within the walls,ultrasonic welding, or using an intermediate material to facilitateattachment. The preferred means of attachment is by sutures.

With reference to FIG. 3, the inner stent 11 includes ends 17 and 19.Bands 21 and 23 depict regions adjacent the ends 17 and 19,respectively, that are coated or otherwise provided with a radio-opaquematerial that shows up as a dark area impenetrable by X-rays. With thebands 21, 23 so applied, the location of the inner stent 11 is clearlyvisible within the vascular system of the patient by viewing it with anX-ray device.

As seen in FIG. 4, when the stent 10 is to be implanted within thepatient, the cover 13 is folded and pleated in the manner shown in FIG.4 so that it lies closely against the inner stent 11 in the collapsedstate thereof providing the smallest possible cross-section tofacilitate conveyance of the stent 10 with a balloon catheter 25contained therein (FIG. 4).

The stent 10 may be conveyed to the site of installation using anydesired well known method such as those described in U.S. Pat. Nos.5,100,429 and 5,275,622.

The inner stent 11 may be made of any suitable material and the covermay be woven or otherwise fabricated.

With reference to FIG. 5, the inner stent 11 is seen with a deliverydevice 1 contained therein. With reference to FIG. 6, the cover 13 isseen to be installed over the inner stent 11 and comprises anintermediate stent layer.

FIG. 7 depicts, schematically, a blood vessel 2 in which the deliverydevice 1 has been inserted with the stent 10 placed thereover. The cover13 is folded or otherwise pleated to closely conform to the outersurfaces of the inner stent 11 as also seen in FIG. 4. To secure thecover or intermediate stent layer 13 over the inner stent 11, aplurality of clips 30 are mounted over the cover 13 at spaced locationsthereover and are in a collapsed configuration tightly holding the cover13 over the inner stent 11. These clips 30 may, if desired, be made of amaterial such as NITINOL.

With reference to FIG. 8, the delivery device 1 has expanded the stent10 at the desired location within the blood vessel 2. As is clearly seenin FIG. 8, the clips 30 have expanded as has the cover 13 and innerstent 11 so that the entire sandwich is now securely mounted within theblood vessel 2 at the desired location.

With reference to FIGS. 9 and 10, two alternatives are depicted forsecurement of the cover 13 over the inner stent 11. In FIG. 9, the innerstent 11 is seen to be concentrically disposed within the cover 13.Sutures 33 of substantially equal length suspend the inner stent 11concentrically within the cover 13. As should be understood, FIG. 9depicts a cross-sectional view similar to that of FIG. 2. As such, aseries of sutures 33 longitudinally spaced along the axis of elongationof the stent 10 are suitably provided.

With reference to FIG. 10, the inner stent 11 is seen non-concentricallysupported within the cover 13. For this purpose, sutures 35, 37, 39 and41 suspend the inner stent 11 non-concentrically within the fabric cover13. As shown, the sutures 35 and 39 may be of similar lengths and thesuture 37 is extremely short in length while the suture 41 is extremelylengthy. As is the case concerning the description in FIG. 9, FIG. 10depicts a cross-sectional view similar to that of FIG. 2. As such, itshould be understood that the sutures 35, 37, 39 and 41 depicted in FIG.10 are merely representative of a series of sutures longitudinallyspaced along the axis of elongation of the stent 10.

FIGS. 11 and 12 depict an alternative embodiment of the presentinvention including a stent 50 having an inner stent 51, a cover orintermediate stent layer 53 and an outer securement device or outerstent 55 consisting of a wire wound in a spiral fashion about theexternal surface of the cover 53 to secure the cover 53 about the innerstent 51. A delivery device 3 is also shown inserted within the innerstent 51. If desired, the wire 55 may be made of a material such asNITINOL.

FIG. 12 shows a blood vessel 4 in which the delivery device hasdelivered the stent 50 to a desired location of use and has expanded thestent 50 at that location. The cover 53 as well as the inner stent 51and outer or securement device 55 are clearly depicted having beenexpanded into the installed location within the blood vessel 4.

In the embodiments of the present invention depicted in the drawingfigures, the stents are shown as being balloon expandable. If sodesired, the stent may also be self-expandable, thermal memoryexpandable, or a combination of the three. In one embodiment, the insidestent can be balloon expandable while the outside stent isself-expandable. Or, the inside stent can ne self-expandable, while theoutside stent is thermally expandable. Yet, the inside stent can bethermally expandable while the outside stent can be balloon expandable.

The sandwich structure of the present invention causes a mutualinteraction between the stent layers permitting uniform expansion. Theclips illustrated in FIGS. 7 and 8 or, alternatively, the spiral wireillustrated in FIGS. 11 and 12, allow the cover to expand slowly anduniformly thereby maintaining integrity of the stent assembly. The innerstent 11 or 51 is continuous in structure while the cover and outerstents or clips are non-continuous. The elastic material of the innerstent may be made of a biological or synthetic material and is intendedto provide a mechanical barrier. The degree of elasticity of thismaterial may be greater than the degree of elasticity of the stents. Theelastic deformation of the material is determined by the elasticdeformation of the inner stent and the outer stent layers. If the innerstent is self-expandable, made of a material such as NITINOL, then thedelivery device would not be a balloon. Rather, an "insertion catheter"would be used as the delivery mechanism.

As such, an invention has been disclosed in terms of preferredembodiments thereof which fulfill each and every one of the objects ofthe present invention as set forth hereinabove and provides a new anduseful sandwich stent of great novelty and utility.

Of course, various changes, modifications and alterations in theteachings of the present invention may be contemplated by those skilledin the art without departing from the intended spirit and scope thereof.

As such, it is intended that the present invention only be limited bythe terms of the appended claims.

I claim:
 1. A stent assembly comprising:(a) An inner continuous stentextending along the entire length of the assembly having spaced uncuffedends; (b) a fabric cover over the entire inner continuous stent, thecover affixed only along a single longitudinal axis outside the innerstent to at least two point along the inner continuous stent; (c) thefabric cover having an expansible outer stent in the form of a pluralityof cylinder clips collapsed over the fabric cover to secure the fabriccover to the inner continuous stent; (d) the outer stent having a lesserlongitudinal length than the inner stent; and (e) an outer diameter ofthe inner stent being substantially equivalent to an inner diameter ofthe fabric cover.
 2. The stent assembly of claim 1, wherein the innerstent is tubular.
 3. The stent assembly of claim 1, wherein the cover isaffixed to the inner stent along a line parallel to a longitudinal axisof the inner stent.
 4. The stent assembly of claim 1, wherein the innerstent is secured concentrically within the cover.
 5. The stent assemblyof claim 1, wherein the fabric cover comprises an intermediate stentlayer having a diameter larger than a collapsed diameter of the innerstent.